Soap-salt complex grease containing n-acyl p-aminophenol



SOAP-SALT COMPLEX GREASE CONTAINING n-ACYL p-AMHNOPHENOL Arnold J. Morway, Rahway,-N. 5., assignor to Esso Research and Engineering (Iompany, :a corporation of Delaware No Drawing. Application April 30, 1954 SerialN'o. 426,927

12 Claims. (Cl. 252-40.?)

This invention relates to improved lubricating grease compositions having suitable characteristics for operation at elevated temperatures. In particular, the instant invention relates to lubricating grease compositions having outstanding high temperature properties which comprise complex alkaline earth soap greases wherein the soap system consists of a combination of the soap of high and low molecular Weight fatty acids, the low molecular weight acid predominating, which contains combined therein a minor but stabilizing proportion oi an-n-acyl p-aminophenol.

High temperature lubricating grease compositions which are prepared'by thickeninga lubricating oil with a complex soap-salt system wherein the salt component 'predcniinates'have'been described'in the art. However, these excellent high temperature lubricating grease compositions tend to harden excessively on storage. There first appears on the surface of these complex greases a hard crust which gradually extends throughout the body of the grease. lt'has been proposed to eliminate-this crust formation and hardening effect by the incorporation of minor amounts of hydroxy fatty acids such as the monoor di-hydroxy stearic acids, hydrogenated castor oil and the like.

It has now been found and forms the .object of this invention that the tendency to harden noted in these soap-salt complex greases maybe substantially eliminated by the inclusion in the grease composition of minor amounts of a class of compoundsreferred to as the n-acyl p-aminophenols, .to be more completely described-below.

The following series of-examples illustrate the inventive concept.

EXAMPLES 1 AND 2 Preparation.'ihe oil, lime and Hydrofol acid are charged to a'fire heated kettle and warmed'to 135 F., at which time the acetic acid is charged. The temperature is then raised to 500 F., and the grease cooled while stirring to 300 F. The n-stearoyl p-aminophenol'is added and the grease cooled to 250 P. where the phenyl alpha-naphthylamine is charged and the grease further cooled to 200 F. The'grease is 'then hon'iogeriized' and filtered. Comparative 'dataare set out'inTabl'e 'I below.

Table I Properties Example 1 Example 2 Appearance Excellent, smooth, uniform products Penetration 77 F 200 195 297? 238 Worked 100,000 st 295 '308 Dropping Point. None None Wheel Bearing Test. 6 hours Pass Pass (no leakage) Norma-Hoffman Oxidation: Hours to 5 p. s. i.

drop in oxygen pressure 1 468 .320 Penetration after 1 W storage:

Unworked 205' 185 Worked 60 stro 291 216 Penetration after 3 mon UnworkecL 199 1 Worked 60 stro 288 '155 1 With no phcnyl alpha-naphthylamine present in composition on the flame test, the time (hours) to a 5 p. s. i. drop in oxygen pressure was 468 ours.

2 Heavy crust on grease.

It will be noted that the inclusion of the n-stearoyl p-aminophenol in the grease composition of Example 1 completely eliminates the crust formation which was found to exist in Example 2. I is also to be noted that when the phenyl alpha-naphthylamine was omitted from Example 1, the Norma-Hoffman oxidation test gave-the same results showing that the n-stearoyl p-aminophenol served a dual function.

EXAMPLES 3 AND 4 Preparati0n.--'Charged oil, fatty acids-and lime to a fire heated kettle and warmed While agitatingto P. Then added the acetic acid and continued heating to 500 F. Cooled while agitating to 300 T Added N-lauroyl p-arninophenol and cooled to 200 F. The grease was homogenized and filtered. Comparative data areset out in Table 11 below.

Table 11 Example 3 Example 4 Properties e a b a (1 Percent free alkalinity (as N aOH) 0.08 0. 42 0.32 0.21 .Appearauce Excellent, smooth, uniform Penetrations 77 F. mm./l0:

Unworked 255 217 202 195 Worked 60 strokes. 269 242 258 238 Worked 100,000strokcs 300 330 295 308 Wheel Bearing Test: 6 hours at 220 F". Pass (no Ieakag e) Norma-Hofiman Oxidation: Hours to 5 p. s. i. drop 372+ 34 .35 28 AFBMA-NLGI Lubrication Life Test:

10,000 R. P. hi. at 250 F"; 556 610 A32 527 Dropping Point, "F None None None "None enetration after 1 week storage Unworked 252 200 200 .185 Worked 60 strokes 263 220 259 216 Penetration after'3 months storage:

U nworked 250 199. #120 W'orked 60 strokes 270 159' 265 1 Heavy crust formation on grease surface.

When the dataon oxidation life and structure after;

storage is examined the advantage ofincorporation of the N-acyl p-aminophenol becomes quite apparent (Examples 3a and 4a versus Examples 3b and 4b),

The N-acyl aminophenols incorporated in the grease compositions of this invention have the following general formula: 7

alkyl groups containing from 1 to carbon atoms. I

The, preferred embodiment of this invention contemplates theuse of compounds, according to the formula 7' above, wherein Rfand R" are hydrogen atoms'and wherein Ris a straight chain aliphatic group containing from 12 to 22 carbon atoms. Exemplary of these preferred 7 compounds are N-lauroyl p' aminophenol, N-palmitoyl p- I aminophenol, N-stearoylp-aminophenol, N-arachidoyl paminopheuol and N-behenoyl'p-arninophenol. N-lauroyl p-aminophenol, N-stearoyl and N-palrnitoyl p-aminophenol or mixtures of these are especially preferred. a

- The. alkylated acyl' paminophenols exemplified'by the formula above 'whenR' and R"are alkyl groups con-T taining from 1 to20 and preferably from 4 to 15 carbon atoms, are also operable, Compounds such as N-nvaleryl- 4aminoa3:pentadecyl. phenol, (N-n-pentanoyl-4- aminO B pent'adecyl phenol), N-n-prQpanoyll-amino-S- pentadecyl phenol, N-n-pentanoyl-4-amino-2,6-di-tert.-

. butyl phenol; N-n-hexyl-4-aminoQ-hexyl phenol; are ex operable, The .is'o compounds, such as those obtained from Oxo acids, are also contemplated.

f plished by simply admixing the desired acid with the 'desired p-aminophenol and heating the mixture under proper a The reaction progresses smoothly The preparation of these acyl p-aminoph'enols is accomreaction conditions. 7 (splitting off I water) giving the desired acyl p-aminophenol whichmay be purified by any of the various rnethods known to the art such as distillation, crystallization,

extraction, etc;

The high metal content soap salt complexes containing i carboxylic acid for each mol of saponified high molecular the metal salt of at'least 7 mols of'a low molecular weight weight acid as described above may be incorporated into a wide variety of lubricating oils either naturally occurring 7 or of synthetic origin. 7 These soa complexes may be of the'present invention are; those having 12-30 carbon combined with mineral orsynthetic lubricating oils in grease making proportion. that is to say, containing from i 5 to weight percent of the complex soap The high molecular weight'acids useful for the purposes atoms and preferably those-having 14-22 carbonatoms perv molecule. These-acids 'may'bederived from saturated or unsaturated naturallv'occurring or synthetic fatty .ma

' 'terialsr LThe fatty acids normally used inthe manufacture o f'conventional, reases; :particularlvjthe more saturated acidsfare' preferred. Examples of'fsuch acids include st'earic, hy droxyrstearic such as, l2 hydr'oxy ,stearic, di-hydroxy stearic, poly-hydroxv'stearicrand other 1 saturatedhydroxy fatty acids, arachidic, hydrogenated i. fish oil and tallow acids, etc Unsaturated; acids; such as oleicgri'cinoleic and similar acids may likewise be used? -Suitable low molecular weight acids include s'atura ted f aud unsaturated aliphatic monocarboxylic acids having about 1-6 carbon atoms, such as formic, acetic, propionic,

forbid-acrylic, and similar acids including their hydroxy derivatives, such as lactic acid, etc, Formic and, 'partic- I a rlv ne m. pee V V V The 'choice'of the metal" component depends to a certain extent on the useifor which the compl x soap. of the invention is contemplated/ The alkalineearth metals, particularly calcium, strontium, barium and magnesium are useful for'many purposesof the invention. These metals afford greatest advantages when used as thickeners V .3 inthe manufacture of greases because they, permit the production'of greases having outstanding load-carrying characteristics and satisfactory structural stability at high temperatures and under mechanical stress even-without even .when added to the oil dispersant in relatively high proportions.

The high metal content soap-salt complexes of the invention may be prepared by coneutralization of 'a mixture metals desired.- This coneutralization'ste'p may be carried out iusituin the liquid menst'ruum'to which the complex soap isfto he applied in actualusef For example, the 'mixe'dacids may be coneutralized in a portion orall of the lubricating oil' forming the dispersant of a grease to be thickened by? the'complex soap. Similarly, the coneutrali zation may be carried out infuel .oil or other dispersant .or solvent fluids. Coneutralization is particularly desirable in casesin which the soap and salt have thesarne; metal constituent. Usually the coneutralized material is heated-to high temperatures of about 450 550 F. or

higher, prior to use, to, dehydrate the product and to promote formation of the complex.

- heat treatment and the heating step should becarried out under pressureI V A V Instead 'ofusiirg-high 'molecular weight fatty acids proper, esters'thereof, particularly the glycerides or other' acidogenic materials such as the nitriles, mayserve as the startingmaterials, Naturally occurring animal "or;

' vegetable fats. and'oilsare preferred materials of this J type. iAlso, the low molecular weight carboxylic acids may be employed in the form of suitable esters, such as those of g lycerine, ethanol. etc., 'or other acidogenic fcom- Conventional conditions conducive to the saponificationof these esters followed ,7 by"dehydration and alcohol removal "may 'be' usedp' I Esters of this type maybe used as described inthecase j of c oueutraliz ation as well as in the'case of separate pounds, such as the nitriles.

' formation or the soap and salt described below.

' The high'metal cfontent soap-salt complexes of the in-f 7 ventionrmay also be prepa'redyby separatelypreforming "at least a portion of the high molecular weight acid soap and/or 'thelow molecular: weight carboxylic acid salt and intimately mixing the soap with the salt,' followed by i heating, it necessary. 7 This' method is useful particularly when different inetalslarefemployedas bases for'the' soap and'salt constituents respectively.

60 i The choice of'the'material to which t'he high metal con-Y tent complex soaps of the inventionar'e applieddepends,v

. of course,.on theuseicontemplated. Forfgreas'e manu- 1 facture, in accordance with the inventiqn mineralas well as synthetic lubricating. oils may be nse dincluding well-f 7 known di-es ters', complex esters, hydrocarbon polymers,

. silicone oils, polyglycol,derivatives, etc. iQuite general-i. V 1y, these oils should have a viscosity within-therangeof a. about 3 5-200. SUS at 210 and flash points of about 3509-600 F. A, viscosity index'of IOO-Orhigher may i 70 be employed; however, oils iof'lower viscosity findex,

such'a's below "V1. I. gi e better yields. 1,It has alsow been found that SOQD SflllI COlIlPlCXQS containing' more than 30' mols, e. g. 3040. mols of low. molecular weight Q 7 'si cid for geachmolbfhigh molecular weight acid havcfi; e 5' particular,utility'forconverting synthetic oils or the ester:

of the high and low molecular weight acidswith suitable bases, particularly the hydroxide and/ or carbonates of the When this heating: step iscarried out'in a liquiddispersantthe latter'should amples of the alkylated acyl p-aminophenols which are P a boiling Point above lhelheatillg temperature 0' the 'agsagaac type into excellent -greases. iGomplex :soapiapriiportions of about 5-30'wt.1percent, ;;preferably :about 8-20 wt. percent, based on total grease may be used in preparing the improved greases of the invention.

To summarize briefl the instant invention relates to new and improvedlfib'ricating grease compositions which have a high degree of storage stability. These novel lubricating greases comprise a lubricating oil, either naturally occurring or synthetic, with a minor but grease thickening amount of a soap-salt complex. This complex comprises the alkaline earth metal soap of a high molecular weight fatty acid having from about 12 to about 30 carbon atoms, preferably about 14 to about 22 carbon atoms, and an alkaline earth metal salt of a low molecular weight fatty acid such as acetic acid, formic acid, furoic acid, propionic acid, acrylic acid, and the like; that is to say, those low molecular weight acids having from about 2 to about 6 carbon atoms. Formic acid and acetic acid salts of alkaline earth metals are preferred. The ratio of the low molecular weight salt to the high molecular weight soap should be within the range of from about 7.5:1 to 20:1, preferably from about 9:1 to 15:1. From about 50 wt. percent to 30.0 wt. percent, preferably from about 8.0 wt. percent to 20.0 wt. percent of the total complex may be used.

Included in the grease formulation, and directly responsible for the high degree of structural stability is a minor but stabilizing amount of an N-acyl p-aminophenol. From about 0.5 wt. percent to about 10.0 wt. percent, based on the weight of the total formulation of the phenol is used, with from 1.0 wt. percent to 6.0 wt. percent being especially preferred. The N-acyl p-aminophenol has the general formula wherein R is an alkyl group containing from to 22 carbon atoms, preferably 12l8 carbon atoms, and wherein R and R are selected from the group of hydrogen atoms and alkyl groups containing from 1 to 20 carbon atoms, preferably from 3-12 carbon atoms. Especially preferred, and contemplated in the preferred embodiment of the invention, are those N-acyl p-aminophenols according to the general formula above wherein R and R" are hydrogen and wherein R is an alkyl group containing from 12 to 18 carbon atoms, such as N-lauroyl p-aminophenol, N-stearoyl p-aminophenol and the like.

It is to be understood, of course, that other commonly known grease additive materials may be incorporated in the greases of invention without departing from the inventive concept. Such materials as tackiness agents, coloring agents, oxidation inhibitors, and the like may be incorporated with the greases as described above with advantage.

What is claimed is:

1. A lubricating grease composition which comprises a major proportion of a lubricating oil and a minor but grease thickening amount of a soap-salt complex, said complex comprising an alkaline earth metal soap of at least one high molecular weight fatty acid with an alkaline earth metal salt of a low molecular weight monocarboxylic acid containing from 2 to 6 carbon atoms, the molar ratio of said salt to said soap in said complex being between about 7.5:1 to 20:1, said lubricating grease composition containing a minor amount sufiicient to eliminate crust formation and hardening of a material of the formula 6 wherein R zis -an alkyl group of Ifrom 10 tof2-2 carbon atoms and wherein-1R andR" areeachselected from the group consisting of hydrogen atoms and alkyl groups containing from 1 to 20 carbon atoms.

2. A lubricating composition according to claim 1 wherein said alkaline earthmetal is calcium.

3. A lubricating grease composition according to claim 1 wherein said low molecular weight acid is acetic acid.

4. A lubricating grease composition according to claim 1 wherein R and'R of the formula "are hydrogen atoms and wherein R of the formula is an alkyl group containing from 12 to 18 carbon atoms.

5. A lubricating grease composition comprising a major proportion of a lubricating oil and a minor but grease thickening amount of a soap-salt complex which comprises the calcium soap of at least one high molecular weight fatty acid having about 1230 carbon atoms and calcium acetate, the molar ratio of acetic acid radical to high molecular weight fatty acid radical in said complex being between about 7 .5:1 to 20: 1, said lubricating grease composition containing a minor amount sufficient to eliminate crust formation and hardening of a material of the formula wherein R is an aikyl group of from 10 to 22 carbon atoms and wherein R and R" are each selected from the group consisting of hydrogen atoms and alkyl groups containing from 1 to 20 carbon atoms.

6. A lubricating grease composition according to claim 5 wherein from 8.0 to 20.0 weight percent of the complex is used.

7. A lubricating grease composition according to claim 5 wherein said high molecular weight fatty acid is hydrogenated fish oil acid.

8. A lubricating grease composition according to claim 5 wherein the molar ratio of said acetic acid radical to said fatty acid radical is from 9:1 to 15:1.

9. A lubricating grease composition according to claim 5 wherein R of the formula is an alkyl group of from 12 to 18 carbon atoms and wherein R and R" of the formula are hydrogen.

10. A lubricating grease composition which comprises a major proportion of a lubricating oil containing combined therein from about 8.0 weight percent to about 20.0 Weight percent, based on the weight of the total composition of a soap-salt complex, said complex comprising calcium acetate and the calcium soap of hydrogenated fish oil acids, the molar ratio of said calcium acetate to said calcium soap being about 9:1 to 15:1, said lubricating grease composition containing about 1.0 weight percent to about 6.0 weight percent of N-lauroyl p-aminophenol.

11. A lubricating grease composition which comprises a major proportion of a lubricating oil containing combined therein from about 8.0 weight percent to about 20.0 weight percent, based on the Weight of the total composition of a soap-salt complex, said complex comprising calcium acetate and the calcium soap of hydrogenated fish oil acids, the molar ratio of said calcium acetate to saidv calcium soap being about 9:1 to 15:1, said lubricating grease composition containing about 1.0 weight percent to about 6.0 weight percent of N-stearoyl p-aminophenol.

12. A method of inhibiting hardening and crust formation of 'a soap-salt complex thickened grease wherein said complex comprises alkaline earth metal soap of high molecular weight fatty acid and alkaline earth metal salt of C to C fatty acid, the molar ratio of said salt to said soap being about 7.5 :1 to 20:1, which comprises iizcbrpoifi fi g into said grease: bdiis-Oj to 16.0 W t. 7 percefn't of amatsrialhaving the formula: V

wherein R is a C to'C selected from the group vit C alkyl groups.

n V V *7 V V V V 7 alkyl group arid R and R" are consisting o f'hydr ogsn 'and C 10 7 s f 'Be fergncesciged in th hfile 9f this patent 1 QMTE SI TE I N S 

1. A LUBRICATING GREASE COMPOSITION WHICH COMPRISES A MAJOR PROPORTION OF A LUBRICATING OIL AND A MINOR BUT GREASE THICKENING AMOUNT OF A SOAP-SALT COMPLEX, SAID COMPLEX COMPRISING AN ALKALINE EARTH METAL SOAP OF A LEAST ONE HIGH MOLECULAR WEIGHT FATTY ACID WITH AN ALKALINE EARTH METAL SALT OF A LOW MOLECULAR WEIGHT MONOCARBOXYLIC ACID CONTAINING FROM 2 TO 6 CARBON ATOMS, THE MOLAR RATIO OF SAID SALT TO SAID SOAP IN SAID COMPLEX BEING BETWEEN ABOUT 7.5:1 TO 20:1, SAID LUBRICATING GREASE COMPOSITION CONTAINING A MINOR AMOUNT SUFFICIENT TO ELIMMATE CRUST FORMATION AND HARDENING OF A MATERIAL OF THE FORMULA 